There has recently been considerable activity in the production of fiber reinforced plastic leaf springs for vehicles due to the substantial reduction in weight as compared to metal leaf springs. Fiber reinforced plastic leaf springs can be produced by winding fibrous strands impregnated with a thermosetting resin around a pair of spaced bushings. After the desired number of windings have been made to produce the required strength characteristics, the wound structure is placed in a mold and the thermosetting resin is cured. The resulting cured product consists of a generally curved central section and integrally connected end portions having openings or eyes adapted to receive connecting members.
In other methods of manufacture, the curved central section of the leaf spring is molded separately from resin-impregnated fibrous material, and after molding, the ends of the central section are mechanically connected to metal end members having openings to receive connectors that connect the spring to a vehicle.
It is desired that the curved central section of the spring have rounded, longitudinal edges because sharp edges tend to produce high stress areas. Rounded bottom edges can readily be produced in the molded structure by utilizing rounded corners for the female mold. However, in the past rounded upper edges have not been satisfactorily produced by molding. Grinding away the molded sharp upper edges acts to remove and sever the reinforcing fibers which reduces the strength characteristics of the spring.
In any molding operation flash is produced at the parting line between the male and female molds. When molding a fiber reinforced plastic leaf spring, some fibers are carried into the flash and after molding, on removal of the flash, these fibers are ground away. If the flash is located at the upper portion of the spring, which is a high stress area, the removal of the flash and severing of the fibers at this location can adversely effect the physical properties of the spring. Furthermore the severed fibers tend to produce sharp needle-like projections which can be a hazard to handling of the spring.